1. Field of the Invention
The invention pertains to the field of organic waste disposal from municipal sewage facilities, feedlots, dairies, poultry barns, swine farms, and the like. More specifically, the organic waste is disposed of by applying sludge or manure to a crop.
2. Description of the Related Art
Various facilities generate or gather organic waste requiring disposal. For example, feedlots, animal barns, agroindustrial plants, municipal sewage plants, and farms that keep large numbers of animals must process enormous quantities of organic waste for disposal, often in the form of liquid manure. The disposal of untreated organic waste potentially pollutes water by adding pathogens. Waste substances contain chemicals and decomposable substances that deplete oxygen in water. Leaching of these substances or direct discharge into water can impair the capacity of the receiving water to support life. Additionally, these facilities may release acrid gasses that are unpleasant to smell and contribute to global greenhouse effects.
In particular, agroindustrial livestock and poultry production methodologies increasingly rely upon centralized facilities having a high animal population density. Immense volumes of excrement build up in these facilities unless they are periodically cleaned. Much heavy manual labor is avoided by providing such facilities with waste disposal systems. For example, U.S. Pat. No. 5,911,195 issued to Tripp et al. describes a swine-raising facility with waste management and recycling. The pigs are raised in stalls having a heated floor with a grating that permits waste to enter gutters. Waste falls or is washed into in the gutters, which convey the waste to a site where liquid manure is sprayed onto straw, sawdust, or another substrate for composting and eventual use as fertilizer. U.S. Pat. No. 6,014,948 issued to Gordon describes a shelter for shading and cooling dairy cows, where the roof structure channels rainwater into the interior of the structure for flushing waste from the feeding area. U.S. Pat. No. 5,195,455 issued to van der Lely et al. describes a sensor-based system that detects the presence of waste and, by the application of loud noises and/or electric shocks, discourages dairy cows from defecating outside a designated area. Electronic devices sense or detect waste that the animals deposit in the defecation area. Waste detection is followed by flushing the waste into a drain system for disposal.
In planning for a National Animal Health Monitoring System (NAHMS) study of the dairy industry during 1996, the United States Department of Agriculture (USDA) surveyed dairies in 20 states to describe current use of animal waste handling systems. The study collected data from 1,219 producers each having 30 or more dairy cows. The producers represented seventy-nine percent of the milk cows in the United States.
Most operations with fewer than 100 dairy cows use some form of solid waste storage (79.2 percent). As herd size increases, solid waste storage methods become less common (59.5 percent in operations of 200 or more cows). Use of methods for storing manure in a liquid form increase with herd size. The two primary storage methods are slurry and lagoon. With the slurry method, manure is stored as a thick liquid in a pit located under the barn floor or in a tank or earth-basin until it is applied onto land. With lagoons, manure is often subjected to anaerobic and/or aerobic microbial digestion, as well as chemical treatment. Manure is diluted with water, e.g., water from flush systems and milking-parlor wash water. Slurry systems are more common than lagoon systems for herds of fewer than 200 cows. Both systems are equally popular among producers with 200 or more cows. Over 90 percent of herds with 200 or more cows have some type of liquid manure storage system. Since evaporation reduces total lagoon volume, especially in more arid parts of the country, so lagoons are most common in the western U.S. Producers with liquid manure systems in the midwest and northeast prefer slurry systems over lagoons.
The USDA study also assessed management practices associated with minimizing environmental consequences of manure applications. Manure nutrient analysis, manure application rates based on crop nutrient requirements, manure incorporation, and no-spreading buffer zones around waterways are four management practices designed to limit environmental impacts of waste handling. Most dairy producers (89.4 percent) use one or more of these manure management practices. Nearly half (43.2 percent) of the producers who applied manure to land indicated that they established manure application rates based on manure nutrients or crop needs. Less than one-seventh (14.0 percent) of producers analyze their cows' manure for nutrient content, however. Producers from larger herds (100 or more dairy cows) are more likely to analyze the nutrient content of their manure than their small herd counterparts.
Manure incorporation into soil within 24 hours minimizes odors and nitrogen loss to the atmosphere. Under one in seven producers with fewer than 100 cows (15.8 percent) incorporate their manure into soil within 24 hours. The percentage increases with herd size to over one-third (38.7 percent) of producers with 500 or more cows. More than three-quarters (78.1 percent) of producers who spread manure reported having buffer zones of 50 feet or more where manure was not spread.
USDA has studied the relationship between good waste management and good milk production management. Dairy producers who used at least three of these waste management practices were categorized into one group. Those who use fewer than three such practices were placed in another. Producers were also grouped into quartiles by their milk production per cow. Producers in the top per-cow production group were twice as likely to use at least three manure management practices than were those in the bottom per-cow production group (32.5 percent vs. 14.7 percent). Thus, the USDA has determined that good waste management practices do not in conflict with milk production per cow. Most dairy producers use at least one management practice designed to limit environmental impacts of dairy waste management.
The practice of flushing animal and human wastes leads to another problem, namely what to do with the effluent material. Governmental agencies including state and local governments, as well as the United States Environmental Protection Agency (EPA), increasingly impose stricter regulatory controls on organic waste sources. Municipal sewer systems have been federally regulated for some time, for example, under the Clean Water Act. Regulatory agencies increasingly recognize that animal waste, if not managed properly, can pollute nearby water bodies. Agricultural runoff is rich in nutrients including nitrogen and phosphorous. These substances encourage growth of dangerous pathogens, such as Pfisteria piscicida, which is frequently responsible for major fish kills, disease events in several mid-Atlantic states, and may pose a risk to human health.
Despite these problems, organic waste has beneficial value when it is used as fertilizer for plants. This waste is preferably treated by a variety of processes to remove pathogens and/or reacted to create useful byproducts. U.S. Pat. No. 4,956,093 issued to Pirbazari et al., describes a wastewater treatment system in which active particulate material, such as activated carbon, mixes with dairy wastes under turbulent conditions after pretreatment with alum or ferric chloride. U.S. Pat. No. 5,709,800 issued to Ross et al. describes using a high temperature reactor to process organic wastes by catalytic reaction, such as a silicate or phosphate-catalyzed reaction with metal nitrites. U.S. Pat. No. 6,503,394 issued to Hoyt describes a system that thermally processes up to 10% of raw organic waste in a digester while the remaining waste is deposited in a lagoon. The digested waste increases the production of methane when fed to the lagoon, and the methane can be gathered for beneficial uses. Wastewater lagoons can be maintained at predetermined conditions for bacterially enhanced digestion, as shown in U.S. Pat. No. 6,071,418 issued to Tai where a stratified lagoon is ozonated to provide an aerobic cap with an anaerobic bottom zone.
The term “liquid manure” describes raw excrement, such as feces and urine, which is sometimes slurried with water, as well as excrement that has been processed by the aforementioned processing systems. Liquid manure contains both solid and liquid components, but has a sufficient liquid content to permit the material to flow. USDA studies have determined that the content of liquid manure varies by:    1. composition of the feed ration;    2. amount of bedding and water added or lost:    3. manure collection, handling and storage practices;    4. method and time of land application;    5. climate; and    6. animal type
Table 1 shows the average nutrient content and range found in dairy manure in the state of New York, and is representative of an average dairy manure:
TABLE 1Solid orSemi-SolidLiquidAverageRangeAverageRangeNutrientlbs/tonlbs/1000 gal.Total N116-17329-63Ammonium-N41-7 152-42Organic-N74-11173-35P2O553-12144-34K2092-15303-56
Liquid manure can be converted into a variety of useful products. U.S. Pat. No. 4,956,093 issued to Halfter describes a system for processing liquid manure to harvest bound ammonia for use in fertilizer, with separation of methane and carbon dioxide byproducts for combustion. U.S. Pat. No. 6,497,741 issued to Sower describes a process for converting the solids content of liquid manure from swine into a granular slow-release fertilizer. In like manner, U.S. Pat. No. 6,171,499 issued to Bouchat describes an advanced municipal and industrial sludge processing plant that produces a granular fertilizer from liquid manure. U.S. Pat. No. 5,885,461 issued to Tetrault et al. describes a system that collects liquid manure from swine and processes the same by physical and chemical techniques to produce a dried sludge that can be safely returned to the environment. U.S. Pat. No. 5,443,730 issued to Letourneux et al. describes a process for the purification of a urban organic wastes. The waste is submitted to a reactor for mixing and reaction with active alumina and lime. A mineral sludge and supernatant effluent are extracted by decantation or filtration. U.S. Pat. No. 5,501,718 issued to Bandurski describes the mixing of manure, sewage, or other organic waste with a carrier to form a substitute for peat moss.
While organic wastes may be treated for reduction of deleterious qualities, and useful products may result, there remains the problem of how to dispense such products. U.S. Pat. No. 5,755,058 issued to Guyot et al. describes the use of a wide spray-boom in dispensing liquid manure and related products over straw or crop residue in a field Loading of this fertilizer occurs, for example, in the range of 1000 gallons to 5000 gallons of liquid manure per acre, where 5000 gallons per acre is understood to be about the limit of tolerance for fertilizer loading. Another apparatus described in U.S. Pat. No. 5,682,829 issued to Sulkup describes a tank filled with liquid manure that is followed by a disk and nozzle assembly used to inject the liquid manure into the soil. U.S. Pat. No. 5,462,232 issued to Vastveit describes a rotating nozzle assembly for use in combination with a liquid manure spreader. A truck-mounted sludge gun may be used to dispense liquid manure or urban sewage wastes over difficult terrain, as described in U.S. Pat. No. 4,515,311 issued to Takata. Alternatively, a drag hose assembly can be pulled by a tractor and used to dispense liquid manure, as disclosed in U.S. Pat. No. 6,427,6123 issued to Huffman. Center-pivot irrigation systems may be adapted to dispense liquid manure suspensions, as disclosed in U.S. Pat. No. 6,138,928 issued to LaRue et al.
Agricultural demand for fertilizer is seasonally driven in specific localities. On the other hand, the production of organic wastes continues in large volume no matter what season it is. Periodicity in demand means that interim plans are required for disposition of such materials, at least on an interim basis between periods of seasonal need for fertilizer. A decision must be made whether to store the wastes or to dispose of them. Either decision may be subjected to complicated regulatory compliance and/or permitting processes, for example, as in the permit and review program provided for in the Minnesota Rules Chapter 7020. When a decision is made to dispose of the wastes by applying them to land, factors taken into regulatory consideration are the nitrogen demand of plants or crops to which the wastes are applied, the drainage capacity of the land, and proximity to contaminable water sources. According to these regulations, a feedlot may choose to grow plants for use in disposing of liquid manure by the application of liquid manure to a field. A maximum amount of effluent loading is permitted, and a factor in determining the maximum amount is the ability of the plants to use the nitrogen. Commercial services are available to test the manure for content in assisting an optimal delivery of manure according to manure content and plant tolerance. The plants tend to exhibit well known effects of fertilizer burning, e.g., browning, death and/or slow growth, if too much effluent is dispensed onto the plants.